The present invention relates to an optical disk device for performing recording and playback of information by focusing a light beam to form a light spot on an optical information recording medium.
The present invention also relates to a focus error detecting device used in an optical recording/playback device performing optical recording and/or playback of information.
The present invention also relates to a device for adjusting the inclination angle of an optical means mounted on an optical disk device or the like.
The present invention also relates to an objective lens drive device mounted on an optical head device for optically recording and/or playing back information on an optical information recording medium.
Prior Art Example 1
FIG. 1 is a schematic diagram of a conventional optical disk device, and FIG. 2 is an enlarged view of information tracks for illustrating the relationship between the information tracks and a groove interference signal in a conventional optical disk device. FIG. 3 shows the focus error signal in the optical disk device in a conventional disk device. FIG. 4 is a schematic diagram showing the focus error signal during track access.
Referring to FIG. 1, an optical head device section 12 comprises a semiconductor laser 2, an objective lens 6, a photodetector assembly 11 (including photodetectors and differential amplifiers). The semiconductor laser 2 emits a light beam 3 which is collimated by a collimating lens 4 into a collimated beam. The light beam is passed through a beam splitter 5, and is converged by an objective lens 6 to form a light spot 7 on an optical disk 1. Focusing coils 8a and 8b drive the objective lens 6 in the direction of the optical axis. There are further provided a converging lens 9 and a focus error detecting optical element 10 such as a cylindrical lens for detecting the focus error of the light spot 7 on the optical disk 1. A photodetector assembly 11 detects an information signal and a focus error signal. Its output 13 indicates the focus error of the light spot 7 with respect to the optical disk 1, and is supplied to a focus control circuit 14.
Referring to FIG. 1, land parts 15 form information tracks where information is recorded, and groove parts 16 are interposed between adjacent land parts 15. A groove interference signal 17 is superimposed on the focus error signal 13 when the light spot 7 scans in the direction in which it crosses the information track. The period for which the groove interference signal continues corresponds to the pitch of the information tracks (the pitch of the land parts or the pitch of the groove parts).
The operation will next be described. Referring to FIG. 1, the light beam 3 emitted from the semiconductor laser 2 is converted to a collimated beam by the collimating lens 4. The light beam 3 is then passed through the beam splitter 5 and is converged by the objective lens 6 to form a light spot 7 on the optical disk 1. The light beam reflected from the optical disk 1 is reflected at the beam splitter 5, and is passed through the focus error detecting optical element 10, and received by the photodetector assembly 11 and converted there into an electrical signal.
Correction of the focus error of the light spot 7 relative to the optical disk can be achieved by detecting the amount of focus error by the use of the focus error detecting optical element 10, the photodetector assembly 11, and applying the output of the photodetector assembly 11 via the focus control circuit 14 to the focusing coils 8a and 8b, to thereby drive the objective lens 6 in the direction of the optical axis.
However, the focus error signal obtained in the conventional optical disk device formed as described above produces a focus error signal containing a groove interference signal 17 superimposed on the component due to the undulation of the optical disk 1, as shown in FIG. 3. The objective lens 6 needs only to follow the undulation component, but it is made to follow the groove interference components 17 as well. This may lead to voltage saturation of the control circuit or the like. In particular, during access to a target information track, the full amplitude of the groove interference signal is superimposed on the focus error signal, with a frequency dependent on the accessing speed, so that it may adversely affect the focus control system. This is illustrated in FIG. 4, in which T2 is an interval in which access is performed, while regions T1 and T3 are intervals in which tracking is performed. It is seen that the groove interference signal 17 is larger during the region T2, and if the frequency of the groove interference signal 17 is high, saturation and oscillation of the focus control system may be caused.